German patent publication DD 228,089 discloses projecting a grating image by projecting grating grooves via a projection objective at an angle not equal to 90.degree. to the surface normal onto the surface to be investigated in order to obtain data from the deformed grating image as to the nature of the topography of the surface. The deformed grating images are reflected from the surface and/or are deformed in a controlled manner. In this publication, the required projection beam path is realized with the aid of an optically complex projection system. This projection beam path lies eccentrically to the optical axis of the projection objective.
A further possibility is to mount an aperture diaphragm eccentrically downstream of the projection light source which, however, leads to a considerable and unwanted limitation of the effective illuminating energy. However, if, and in lieu thereof, the light source itself is mounted eccentrically, then problems result when utilizing such an arrangement in conventional reflected-light microscopes.